Autonomous Robot Localization

ABSTRACT

A location estimation system for use with an autonomous lawn mowing robot, comprises a plurality of synthetic surfaces positioned with respect to a mowable space in an environment, a radiation source coupled to the lawn mowing robot, a detector coupled to the lawn mowing robot and configured to detect radiation reflected by objects in the environment, and a controller configured to controllably direct radiation from the radiation source to scan the environment, and to vary at least one of an output power of the directed radiation and a scan rate of the directed radiation, as a function of detected radiation reflected from one or more of the synthetic surfaces.

TECHNICAL FIELD

This invention relates to autonomous robot localization.

BACKGROUND

Autonomous robots that perform household functions such as floorcleaning and lawn cutting are now readily available consumer products.Commercially successful robots are not unnecessarily complex, andgenerally operate randomly within a confined area. In the case of floorcleaning, such robots are generally confined within (i) touched wallsand other obstacles within the rooms of a dwelling, (ii) IR-detectedstaircases (cliffs) down; and/or (iii) user placed detectable barrierssuch as directed IR beams, physical barriers or magnetic tape. Otherrobots map the dwelling using a complex system of sensors and/or activeor passive beacons (e.g., sonar, RFID or bar code detection, or variouskinds of machine vision).

Some consumer robotic lawn mowers use a similar “invisible” barrier—acontinuous guide conductor boundary (e.g., a boundary wire) forconfining random motion robotic mowers. The boundary wire is intended toconfine the robot within the lawn or other appropriate area, so as toavoid damaging non-grassy areas of the yard or intruding onto aneighboring property. Some consumer robotic lawn mowers use localizationsystems that make use of triangulation to determine the robot positionwithin the boundary. For example, multiple beacons are positioned aroundthe property to be mowed. Signals sent between the beacons and thelawnmower positioned in the property allow the lawnmower to estimate theangles and the distance by calculating time-of-flight to each of thebeacons, and using trigonometry to calculate the robot's currentposition. In another example, the system can triangulate the distance toan object using a fixed-angle laser pointer and a CMOS imager, with abaseline between the two. In such examples, the pixel location of thereceived signal at the imager is indicative of the distance to theobject.

There are several challenges in determining the position of an outdoorrobot within a barrier. The resolution of current commercially availableGPS applications is inadequate for this application (e.g., resolution isinsufficient to prevent the lawnmower from not mowing a flower bed orother “no-mow” zone), particularly in light of tree cover commonly foundin lawns. The variation in terrain also makes it difficult for the robotto “see” boundary markers; tilt or slant in the lawn can cause a movingmower having a sweeping beacon detector to not engage, or miss, abeacon. The additional costs and power requirements to improve thesefactors are important for consumers.

SUMMARY

In some implementations, a location estimation system for use with anautonomous lawn mowing robot, the system comprises a plurality ofsynthetic surfaces positioned with respect to a mowable space in anenvironment, a radiation source coupled to the lawn mowing robot, adetector coupled to the lawn mowing robot and configured to detectradiation reflected by objects in the environment, and a controllerconfigured to controllably direct radiation from the radiation source toscan the environment, and to vary at least one of an output power of thedirected radiation and a scan rate of the directed radiation, as afunction of detected radiation reflected from one or more of thesynthetic surfaces. In further implementations, the controller isconfigured to vary a spin rate of the radiation source. The locationestimation system comprises a modulator coupled to the radiation sourceand configured to modulate radiation emitted from the radiation source.The controller is configured to direct the modulator to vary the outputpower of the radiation source in response to detection of reflectedradiation. The controller is configured to direct the modulator to varya beam focus of the radiation source in response to detection ofreflected radiation.

In further implementations, the location estimation system comprises amechanical scanner that directs radiation from the radiation source toscan the environment. The system comprises a rotational scanner thatdirects radiation from the radiation source to scan the environment. Thecontroller is further configured to compare data indicative of detectedreflected radiation to stored data, and to identify the detectedradiation as radiation reflected from a particular object associatedwith the stored data. The particular object is one of the syntheticsurfaces. The particular object is a stationary non-retroreflectiveobject within the environment. The controller is further configured todirect the radiation source to make a first scan of the environment at afirst scan rate. The controller is configured to direct the radiationsource to make a second scan of the environment at a second scan ratedifferent from the first scan rate. The modulator is configured todirect the radiation source to make a second scan of the environment, alimited portion of the second scan performed at a second scan ratedifferent from the first scan rate. The system further comprises asecond detector of a different wavelength responsiveness than a firstdetector. The radiation source is a laser. The radiation is emittedacross a distributed plane. The plane extends at 45 degrees to a surfacesupporting the autonomous lawn mowing robot. The controller isconfigured to modulate the output power of the radiation source. Thecontroller is configured to perform a scan of the environment and tostore resulting data indicative of reflected radiation detected by thedetector during the scan. The synthetic surfaces are positioned atlocations bordering the environment. The radiation source scans during amotion of the autonomous lawn mowing robot. The controller is coupled tothe autonomous lawn mowing robot.

In other aspects of this disclosure, a method of estimating a locationof a self-propelled lawn mowing robot in an environment, the methodcomprises positioning a plurality of synthetic surfaces at locationswith respect to a mowable space in an environment, and placing a lawnmowing robot in the environment, the robot comprising: a radiationsource coupled to the lawn mowing robot, a detector coupled to the lawnmowing robot and configured to detect radiation reflected by objects inthe environment, and a controller configured to controllably directradiation from the radiation source to scan the environment, and to varyat least one of an output power of the directed radiation and a scanrate of the directed radiation, as a function of detected radiationreflected from one or more of the synthetic surfaces. In the method thecontroller is configured to control the controller to vary the scan rateof the radiation source. Also included can be a modulator coupled to theradiation source and configured to modulate radiation emitted from theradiation source. The controller is configured to direct the modulatorto vary the output power of the radiation source in response todetection of reflected radiation. The controller is configured to directthe modulator to vary a beam focus of the radiation source in responseto detection of reflected radiation. The modulator scans a portion of asecond scan at a scan speed different from at least a portion of thescan speed of a first scan. Positioning a plurality of syntheticsurfaces comprises positioning the surfaces at locations bordering theenvironment. The controller scans the environment during a motion of therobot. The motion of the robot includes a grass cutting action.

In further implementations, an autonomous robot comprises a bodyconfigured to move over a surface, two driven wheels carried by the bodyand defining a transverse axis, with each wheel carried on a respectiveside of the body, a radiation source coupled to the autonomous robot, adetector coupled to the autonomous mowing robot and configured to detectradiation reflected by objects in the environment, and a controllerconfigured to controllably direct radiation from the radiation source toscan the environment, and to vary at least one of an output power of thedirected radiation and a scan rate of the directed radiation, as afunction of detected radiation reflected from one or more of syntheticsurfaces placed in the environment. In some embodiments, the controlleris configured to vary the scan rate of the radiation source. A modulatorcoupled to the radiation source is configured to modulate radiationemitted from the radiation source. The controller is configured todirect the modulator to vary the output power of the radiation source inresponse to detection of reflected radiation. The controller isconfigured to direct the modulator to vary a beam focus of the radiationsource in response to detection of reflected radiation. A blade isattached to the body. An odometer is in communication with the wheels,wherein the controller is further configured to compare the position ofthe robot resulting from the identified radiation to a position of therobot indicated by the odometer. The controller is further configured todrive the wheels so as to change a trajectory of the robot in responseto determining the robot position. The radiation source scans during amotion of the robot.

In further implementations, a location estimation system for use with anautonomous lawn mowing robot comprises a plurality of reflectivesurfaces positioned with respect to a mowable space in an environment, aradiation source coupled to the lawn mowing robot, a detector coupled tothe lawn mowing robot and configured to detect radiation reflected byobjects in the environment and radiation reflected by the plurality ofreflective surfaces, and a processor configured to: identify a signalreceived by the detector as being associated with one of the pluralityof reflective surfaces, compare signals received by the detector atlocations near the identified signal to determine environmentalcharacteristics based on radiation reflected by objects in theenvironment, and determine which of the plurality of reflective surfacesgenerated the signal received by the detector based on the comparison.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic view of an autonomous mobile mowing robot placedon a lawn to be mowed,

FIG. 1B is a schematic side view of an autonomous mobile mowing robot,

FIG. 1C is a schematic top view of an autonomous mobile mowing robot,

FIG. 2 is a schematic view of an autonomous mobile mowing robotdetecting retroreflective beacons,

FIG. 3A is a schematic view of an autonomous mobile mowing robotdetecting the environment at a first pose,

FIG. 3B is a schematic view of an autonomous mobile mowing robotdetecting the environment at a second pose,

FIG. 4A is a schematic view illustrating a variable scan rate used bythe autonomous mobile mowing robot of FIG. 1B,

FIG. 4B is a schematic view illustrating a multivariable scan rate usedby the autonomous mobile mowing robot of FIG. 1B,

FIG. 5 is a flowchart describing a method for using a variable scanrate,

FIG. 6 is a schematic view illustrating a variable power level used bythe autonomous mobile mowing robot of FIG. 1B.

FIG. 7 is a flowchart describing a method for implementing the variablepower level used by the autonomous mobile mowing robot,

FIGS. 8A and 8B are side and top views of an autonomous mobile mowingrobot detecting its environment with a horizontally fanned laser,

FIGS. 9A and 9B are side and top views of an autonomous mobile mowingrobot detecting its environment with a vertically fanned laser, and

FIGS. 10A and 10B are side and top views of an autonomous mobile mowingrobot detecting its environment with a diagonally fanned laser.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring to FIGS. 1A-1C, an autonomous robot lawnmower 10 is configuredto mow a lawn 20. The autonomous robot lawnmower 10 moves about the lawn20 and cuts grass 22 as it is traversing the lawn 20. The robotlawnmower 10 includes a robot body 100, a surface treater 120 secured tothe robot body 100, a sensor system 130 having at least one surfacesensor 131 carried by the robot body 100 and responsive to at least onesurface characteristic, and a drive system 140 including at least onemotorized wheel 145. In some examples, the wheel may include a tire, orbe a continuous tread or track tread. The drive system 140 is carried bythe robot body 100 and configured to maneuver the robot lawnmower 10across lawn 20. In this example, the surface treater 120 is areciprocating symmetrical cutter. The robot body 100 also supports apower source 160 (e.g., a battery) for powering any electricalcomponents of the robot lawnmower 10, including the drive system 140,the surface treater 120, and a navigation system. When not mowing thelawn 20, the robot lawnmower 10 may be docked at a base station or dock12. In some examples, the dock 12 includes a charging system forcharging the battery 160 housed by the robot body 100.

A data processor or controller 150 having a memory 151 is attached tothe robot body 100 and communicates with and controls a radiation source180 also attached to the robot body 100. The radiation source 180 canone of several types of radiation used for robot navigation, such as alidar (light or laser) source, or a radar source. Laser or radar sourcesare particularly advantageously suited for use in the navigationembodiments described herein. In some examples, the radiation source isattached to the robot on a rotating platform or other scanner that isconfigured to cause the beam to scan about the environment inpredetermined angular increments (e.g., one degree increments).

The controller 150 also communicates with a modulator 185 coupled to theradiation source. The modulator 185 modulates the radiation emitted fromthe radiation source 180. For example, the modulator 185 can modify thebeam focus, the beam power, and/or range of the beam of radiationsupplied by the radiation source 180 and emitted by the robot lawnmower10. The radiation source 180, modulator 185, and controller 150 are alsoin communication with a radiation detector or receiver 190 that detectsincoming radiation incident on the robot lawnmower 10. As shown in FIGS.1B-1C, the robot lawnmower 10 can have a first radiation source 180 anddetector 190 pair at the front of the robot body 100 (the front of therobot being in the direction of normal robot motion indicated by arrow90). The first radiation source 180 and detector 190 pair 180, 190 canemit signals 182 toward and detect signals 184 from an approximate 180°region around the front of the robot lawnmower 10. The robot lawnmower10 can also include a second radiation source and detector pair 194, 196at the back of the robot body 100. The rearward radiation source anddetector pair 194, 196 can likewise emit signals 182 toward and detectsignals 184 from an approximate 180° region around the back of therobot. Alternatively, the radiation source and detector can be spacedfrom each other on the robot body 100, rather than co-located as a pair.In some embodiments, the robot lawnmower 10 can have a radiation sourceand detector located on the top of the robot body 100 which can rotateto emit radiation in a 360 degree radius about the robot lawn mower 10.In any of these embodiments, the robot lawnmower is configured toemit/detect signals (e.g., scan) 360° around the robot body 100.

The controller 150 also communicates with the other systems of therobot, e.g., the drive system 140, the surface sensor 131, and thesurface treater 120. The robot lawnmower 10 can also include a userinterface system 170, which allows a human user to see messagesindicating states of the robot lawnmower 10. The user interface system170 is also in communication with the controller 150. In someembodiments, the user interface system 170 is not located on the robotbody 100. Instead, the user interface system 170 can be a standaloneunit, separate from the robot body 100. In other implementations, theuser interface system can be integrated into another device, such as viaa software located on a user's cell phone, tablet, or other device andthe robot can communicate with the user interface via radio; forexample, a Wi-Fi signal over the internet.

Referring to FIG. 2, for mowing operations the robot lawnmower 10 isplaced on the lawn 20 so that it can mow the lawn 20 which is bounded byperimeter 21. The robot lawnmower 10 is constrained to not traveloutside of the perimeter 21. To demark the perimeter 21, one or moreboundary markers 205, 210, and 215 can be placed in or around the lawn20. For example, boundary markers 205, 210, 215 are positioned on thelawn 20 along the perimeter 21. The dock 12 can also function as aboundary marker and include a synthetic retro-reflective surface. Theboundary markers 200 may include lidar retroreflectors, radarretroreflectors, or passive materials/configurations configured toreflect a signal generated by the robot lawn mower 10. In general, theboundary markers 200 are passive devices and do not actively emitsignals. Rather they are positioned to reflect signals emitted from therobot lawn mower 10. In some examples, the boundary markers 200 areretroreflectors, e.g., a device or surface configured to reflectradiation back to its source with a limited amount of scattering.Because the boundary markers 200 are passive, they can provide theadvantage of being independent of a power source and do not have toinclude a battery or be connected to a source of power. While only threeboundary markers 200 are shown in FIG. 2, any number of boundary markerscan be positioned about the lawn 20.

Each boundary marker 205, 210, 215 is positioned at a location, andsituated so as to be detected by the robot lawnmower 10 as the robotlawnmower 10 navigates the lawn 20. To determine its position on thelawn 20, as shown schematically in FIG. 2, the robot lawnmower 10communicates with the individual boundary markers 205, 210, 215. If eachof the boundary markers 205, 210, 215 is available to the robotlawnmower's line-of-sight and within the reach of the signal, the robotlawnmower 10 can determine its pose based on its location relative tothe three or more boundary markers 205, 210, 215.

As shown in FIG. 2, the robot lawnmower 10 can receive a signalreflected from each of the boundary markers 205, 210, 215. In oneimplementation, the boundary markers are passive retroreflectivemarkers. After the robot lawnmower 10 sends a signal from radiationsources 194, 180 and receives the reflected signal via detectors 190,196, the controller 150 can calculate a range and bearing to eachboundary marker 205, 210, 215. The detectors can be e.g., radar antenna,or laser light detectors. In some implementations, the controller canuse trigonometry to better estimate the position P1 of the robot. Insome implementations, dock 12 could also serve as a reflective beacon.

In other implementations, boundary markers 205, 210, 215 can beconfigured as optical corner reflectors, or corner cubes. An opticalcorner reflector is a retroreflector consisting of three mutuallyperpendicular intersecting flat surfaces. Each surface reflects incidentradiation emitted by emitters 180, 194 on the robot lawnmower 10 backdirectly towards the source, e.g., to be detected by the detectors 190,196. Each incoming ray incident on the cube is reflected three times,once by each surface, which results in a reversal of direction. Thethree intersecting surfaces often have square shapes, and can be made ofthree-sided glass prisms.

In general, the pose of the robot lawnmower 10 can be determined basedon the signals reflected by the boundary markers 205, 210, 215. Moreparticularly, the robot lawnmower 10 sends a signal (e.g., a lasersignal) that is reflected by one of the boundary markers. The robotlawnmower 10 can determine the angle between the robot lawnmower 10relative to the boundary marker based on the location at which thesignal is received. Additionally, the robot lawnmower 10 can determinethe distance between the robot lawnmower 10 and the boundary marker 200based on the time-of-flight between the sending of the signal and thereceipt of the reflected signal. Thus, based on the information frommultiple boundary markers 200, the robot lawnmower's pose can bedetermined by trilaterating based on received range/heading informationfrom each of the boundary markers. In general, trilateration is theprocess of determining absolute or relative locations of points bymeasurement of distances, using the geometry of circles, spheres ortriangles. In one example, trilaterating can be based on a least squaresalgorithm using the distance/time-of-flight measurements. In anotherexample, time-of-flight can be measured indirectly by measuring thephase shift between the signal and the receipt of the reflected signal.

In general, reflective beacons do not generate a signal that is uniquelyidentifiable—e.g., the signal from one beacon is not uniquelyidentifiable as originating from that beacon. However, if the systemwere to be able to distinguish between the signals generated by thebeacons, this information could be used to determine the pose of therobot lawn mower. In some examples, the beacons can be configured toreturn a unique which is distinguishable from signals from otherboundary markers. In some implementations, the unique signal can beimplemented with a passive retroreflector, by e.g., a unique size,shape, or pattern to the boundary marker 200 or dock 12 that encodes theparticular boundary marker. The unique signal permits the robotlawnmower 10 to uniquely identify the signal as being associated with aparticular beacon.

In another example, signals and information about the environmentsurrounding the beacon can be used to uniquely identify a particularbeacon. More particularly, the environment around each of the beaconswill differ and therefore generate a different reflective signal. Forexample, if one beacon is located near a tree, the tree will provide aweaker reflected signal at a distance relative to the beacon. Thus, ascan matching process can use the combination of the signal reflectedfrom the beacon and the signals reflected from environmental objects touniquely identify the beacon.

Scan matching involves taking and storing scan data of the environment.In some implementations, the location determination performed by therobot lawnmower 10 includes performing a scan match on three or moreadjacent boundary markers 200, where each of the three or more boundarymarkers 200 are individually identifiable by adjacent scan match data.More particularly, because the beacons are passive, the signal reflectedfrom the beacon itself is not distinguishable from a signal reflectedfrom another beacon. By combining the reflected signal from the beaconwith a reflective signature of a scan around (e.g., 5 degrees on eitherside, 3 feet on either side) of the beacon, the beacon can be uniquelyidentified relative to the other beacons. For example, FIG. 3A shows therobot lawnmower 10 at a first pose P1. The robot lawnmower 10 emitssignals to locate each of the boundary markers 205, 210, 215, as well asthe dock 12. In addition, the robot lawnmower 10 can use the emittedsignal (or emit another signal) to scan the environment, and store theat least a portion of the radiation signature of the environment at thatpose P1 in the robot's memory 151. The radiation signature of theenvironment is due to and is specific for different obstacles within ornear the lawn 20, e.g., radiation signatures 22, 23, 24, 25 due to treesor buildings surrounding the lawn 20. A radiation signature surroundingeach of the beacons can be stored and associated with the beacon. Thus,the robot lawnmower 10 can use the fingerprint (e.g., the radiativesignature) to uniquely identify each of the beacons. The robot lawnmoweressentially takes a “fingerprint” of the environment at pose P1.

As each scan performed by the robot at differing locations on the lawn20 will result in signature reflections of varying strength, the robotlawnmower can determine its position or pose of the robot on the lawn 20by matching the current travel path scan with stored travel path scanscontained in the robot's memory 151.

At the pose P2 of the robot lawnmower 10 in FIG. 3B, the robot lawnmowerhas changed its pose, both position and orientation, compared to thepose P1 of the robot lawnmower 10 in FIG. 3A. The radiation signatures32, 33, 34, 35 of the same surrounding objects with appear different dueto the change in aspect of the robot lawnmower 10. The robot lawnmower10 would search its database to match the current scan at P2 to thescans in memory.

To increase computational efficiency, the robot lawnmower can use alibrary of signatures relating specifically to the boundary markers. Therobot lawnmower 10 can scan the environment near the reflective boundarymarkers and identify specific features in the immediate vicinity of theparticular boundary marker, 205, 210, 215, 12. This narrow scan rangegives a partial fingerprint that is easier to match. To reducecomputational cost the robot lawnmower 10 could be configured to scan areduced signature library, or more quickly scan a library of storedlocations using this specific signature.

In some implementations, each of the retroreflectors can have a uniquesignature based on a unique size, shape, or pattern to the reflectorthat encodes the particular boundary marker. The unique signal permitsthe robot lawnmower 10 to uniquely identify the signal and thus thelocation and orientation of dock 12. Based on identifying this uniqueretroreflector signal, the processor of the robot lawnmower 10 canselect only the scans in memory containing the unique signal. In furtherimplementations, the processor of the robot lawnmower can combineposition information given by the unique signal and a scan match of theenvironment.

To perform scan matching, the robot lawnmower 10 can first “learn” theenvironment by taking scans of the entire lawn 20. In a learning mode,the robot can navigate the lawn, and record the fingerprint signature ofradiation received at different poses on the lawn 20 to build aradiative signature library. A user may direct the robot lawnmower 10during this learning mode. Alternatively, the robot lawnmower 10 cannavigate and scan the environment autonomously, and build a library ofstored scans for later retrieval. In some implementations, the robotlawnmower 10 can continuously update the stored scan library duringmowing operations. This technique can account for variations in thesignature scans due to changes in reflections caused by changes ofobjects in the environment over time.

Referring to FIGS. 3A and 3B, a combined triangulation technique usesscan matching to uniquely identify signals from respective boundarymarkers. The robot lawnmower can determine its general pose bycalculating the angle and distance of the robot lawnmower 10 to thethree or more boundary markers 200. The robot lawnmower 10 can also scanthe environment near the reflective boundary markers 200 and identifyspecific features in the immediate vicinity of the particular boundarymarker, 205, 210, 215, 12. This information can be used to uniquelyidentify and associate the signals with a particular boundary markerthat is in a position. Thus, the use of the scan matching can increasethe accuracy of the determined robot pose.

The triangulation techniques discussed above can potentially incurmultipath error. Multipath error can occur due to objects placed withinthe environment. For example, radiation emitted from the robot lawnmower10 could be reflected of objects such as a car, a bicycle, and then beincident on the robot lawnmower 10 as a false return signal. To accountfor these inaccuracies, robot lawnmower can be configured to performboth the query of the boundary markers 200 as well as a scan match ateach pose of the robot lawnmower 10. The scan match can confirm that thereflected signal is from a boundary marker as opposed to anotherenvironmental feature.

Further embodiments of this disclosure relate to variable control ofparameters of radiation, 196. In a preferred embodiment, the radiationsource is a laser configured to spin about an axis and is connected to acontroller that modulates the spin rate and/or power level of the laser.However, the control methods described can apply to either or both oflaser radiation and radar radiation. The methods are designed to work inconjunction with retroreflectors, radar reflectors, or other reflectiveboundary markers 200. In particular, the arc length between the lasersignals, the emitted signal strength, or both can be modified.

Signal is proportional to the inverse of the radius squared, where theradius is the distance between the robot lawnmower 10 and the objectdetected (e.g., the boundary marker 200). Thus, both strong and weaksignals are incident on the detectors 190, 196, depending on thedistance to the reflected surface. Radius also impacts the noise of theincoming signal, e.g., closer signals are typically less noisy. Inaddition, the surface upon which the light is incident can reflect avarying amount of the signal. For example, the signals reflected byretroreflective beacons are extremely strong, and can be much higherthan signals due to other objects in the environment such as trees orbricks. Thus, a high detected signal can indicate the position of aretroreflector. To account for these variations in signal strength, therobot lawnmower can adjust the radiation emitted. Additionally, if theradiation source is configured to generate a signal at a predefinedfrequency, the likelihood of receiving a reflection from an item locatednearer to the robot is greater than the likelihood of receiving areflection from an item located further away because as the distancefrom the robot increases so does the arc length between the signals.

In one implementation, the robot lawnmower 10 does a first sweep to scanthe lawn 20 at a first rate, and stores the locations of higher signaland/or reduced noise as areas of interest. The robot lawnmower 10 thenperforms a second sweep to scan the lawn during which the robot slowsthe scan and focuses on the detected areas of interest determined by theincrease in signal strength on the first sweep. More particularly, thecontroller issues a command to cause the laser or radar to rotate at aslower rate in the determined areas of interest such that a greateramount of information can be generated in those areas (e.g., the scancan include pings of the laser at smaller degree increments such asevery 0.2-0.75 degrees as opposed to every one degree). In someexamples, a ratio of the degree increments for the pings in the lessfocused (faster spin rate) scan versus the more focused (slower spinrate) scan can be between 0.1 and 0.8, for example, between 0.25 and0.5. To ensure the robot is capturing the reflectors, the robotlawnmower 10 slows the scan around the expected positions of theboundary markers 200 in subsequent scans. The slower the rotation/spinrate, the more likely it is to see a small retroreflector from a furtherdistance (e.g., in FIG. 3B, boundary marker 210 relative to the robotlawnmower 10 at position P2). If the scan rate slows, the robot canintegrate over a longer time span and filter out more noise in order tosee further obstacles. Further, if a scan matching technique is used touniquely identify the boundary markers 200, the slower spin rate cancollect more information about the environmental features surroundingthe beacon due to the higher resolution of the generated data.

In FIG. 4A, the robot lawnmower 10 has completed an initial sweep of theenvironment to detect the boundary markers. For example, a first scaninclude 360 pings of the laser at one degree increments at a rate of 5Hz. Once these areas of interest have been determined, subsequent sweepscan focus on the area of interest, with the controller 150 changing therotation/spin rate of the radiation to sweep areas of interest at aslower rate than areas of non-interest as identified on the first scan(e.g., by slowing the speed at which the laser rotates in areas ofinterest or increasing the speed at which the laser rotates in areas ofnon-interest as compared to the initial speed of rotation). SR5 is ascan rate, which quickly sweeps through the environment. A slowerrotation/spin rate SR1 is used when passing through regions containingthe boundary markers 200, such as the region surrounding boundary marker215. SR1 is slower than SR5. For example, SR1 can be 5 to 30 Hz,typically 10 Hz. SR5 can be 0.1 to 5 Hz, typically 1 Hz.

In some examples, the robot can alternate between fast and slow spinrates. For example, the robot can perform one rotation at a first spinrate to gather detailed information about the robot location. The robotcould then operate using a higher spin rate for the subsequent 5-10rotations. In another example, the spin rate of the laser could bemodified based on the proximity to the edge of the mowable space. Forexample, as the robot lawn mower approaches the boundary of the mowablespace the speed at which the mower is propelled could be reduced. Inaddition, the speed at which the laser rotates could be reduced togather a greater resolution in the data used to localize the robot lawnmower.

In a further embodiment, in FIG. 4B the spin rate is variable based onthe distance to each retroreflector as well as compared to the areas ofnon-interest. Here, SR5 is the fastest spin rate, and quickly sweepsthrough the environment. Boundary markers 205, 210, 215 and dock 12 areall located at different distances from the robot lawnmower 10, and thuseach boundary marker 200 can be scanned at a different scan rate,depending on the distance from the robot at that moment. For example,SR5>SR1>SR2>SR3>SR4, with closer areas of interest scanned at a fasterspin rate than further areas of interest.

Referring to FIG. 5, a process 1000 for varying the rotation/spin rateis illustrated. The method described by 1000 starts at step 1010. Therobot lawnmower 10 sweeps a pass (or fires in a round) doing a scan at afirst rate (step 1020). During this first pass, the scan finds radarnoise or retroreflectors, (i.e. identifies locations of interest). Therobot lawnmower 10 then sweeps a pass with a slower spin rate setting inareas of interest for subsequent scans (step 1030). As the scanprogresses, the robot 10 then determines if the area being scanned at agiven moment is associated with portions of the environment other thanboundary markers (step 1040). If no, the robot lawnmower 10 determinesthat the area being scanned is relatively less interesting, andincreases the spin rate (or otherwise increases arc length between thefirings of the laser in the scan) to relatively higher rates in areasnot identified as containing any object of interest (step 1050). If atstep 1040 the robot lawnmower 10 determines that the area includesboundary markers then it returns to sweeping at a slower spin rate usingthe shorter arc length between the firings of the laser in the scan(step 1030). Thus, the robot can continue to scan with the spin ratevarying for a length of time (e.g., 3 seconds, 5 seconds, 10 seconds)and then re-determine areas of interest by returning to block 1020.

The robot lawnmower 10 can perform the positioning initial sweep atpredetermined time periods or upon the detection of a beacon outside theslow spin rate zone. In some examples, a ratio of the fast spin rate tothe slower spin rate can be between 2:1 and 5:1, e.g., about 2:1, about3:1, about 4:1, about 5:1.

In some additional examples, rather than vary the spin rate during aparticular rotation, the controller can cause the laser to spin with thespin rate alternating between the faster and slower spin rates after aset number of rotations. This can allow the robot to gather moreinformation and potentially determine the robot's pose with greaterdetail during a slow spin rate scan while tracking the robot and anymovements on a basis that is updated more frequently using the higherspin rate scans.

In other embodiments, to optimize object detection, the power level orbeam focus of the radiation emitted from robot lawnmower 10 can bemodulated. Generally, lower power is preferable for identifying objectsnearby than far away and high power is better for detecting signals fromobjects further away. High power output results in noise on closeobstacles, while seeing objects further away clearly. If operating onlow power alone, the robot lawnmower may not be able to detect furtheraway objects. To try and capture the advantages of both power levels(while minimizing the disadvantages) the robot lawnmower 10 can beconfigured to change the power level of the emitted radiation on variouspositions during a sweep.

If strongly reflecting targets are close to the robot (at a givenposition) and the boundary markers 200 are farther away, the robotlawnmower 10 can use the received signal strength for that beacon tochange the power level up or down. For example, the robot may increasethe power level of the signal where the boundary marker 200 is expectedto be, or has previously determined to be located. If the return signalstrength is low, the robot will increase the power in an attempt todetect the boundary marker 200 that has been drowned out by the closer(and therefore higher signal) reflecting target.

Referring to FIG. 6, the power of the radiation emitted by radiationsource (e.g., the laser) on the lawnmower 10 can vary, with first powerlevel (e.g., as shown by circle PL2 which has a greater diameter thancircle PL1) being less than a second power (e.g., as shown by circle PL2which has a greater diameter than circle PL1). The lower power (PL1) isgenerally used for closer obstacles, while the high power (PL2) isgenerally used to identify further obstacles.

Referring to FIG. 7, a method for varying the radiation power level todetermine both near/far and strong/weak signals is illustrated. Method2000 starts at step 2010. The robot lawnmower 10 sweeps a first pass (orfires in a round) at a lower power level (step 2020). During this firstpass, the low power scan finds radar noise or retroreflectors, i.e.identifies location(s) of interest such as the boundary markers 200. Therobot lawnmower 10 then sweeps a pass with a higher power setting inareas of interest (step 2030). As the scan progresses, the robot 10 thendetermines if noise is being detected from nearby objects (step 2040).If not, the robot lawnmower 10 continues sweeping at high power in areasof interest having no noise (e.g., looking for farther away targets)(step 2050). If yes, the robot lawnmower 10 lowers the power in the areathat is detected to have noise (step 2060). The robot lawnmower 10 thendetermines if the area scanned on focuses on areas of interest locatedbeyond the noise range (step 2070). If yes, the robot continues sweepingat high power in areas of interest having no noise (step 2050). If not,then the sweep continues on the next portion of scan (step 2080), andreturns to checking if noise being detected from nearby objects (step2040).

In some examples, a controller 150 in communication with the laser orother radiation source is configured to perform scans at alternatingpower levels. For example, rather than vary the power level during aparticular rotation, the controller 150 can cause the laser to alternatebetween the two power levels after a set number of rotations. This canallow the robot to gather more information and potentially determine therobot's pose with greater detail because both nearby and further awayobjects will be located based on the two different scan power levels.

Retroreflector surfaces such as boundary markers generally have a muchstronger signal than do environmental objects. To account for thediffering strength of detected signals resulting from different objecttypes, as well as from distance, different detection schemes arepossible. For example, detector 190 on the front of the robot body canbe composed of two different detectors. Similarly, detector 196 on therear of the robot body 100 can actually be composed of two detectorsEach pair of detectors can include one detector configured to detectlower power signals and one detector configured to detect higher powersignals. In one implementation, filtered glass placed in front ofdetectors can attenuate the signal incident on the detectors making itmore tuned to detecting high signals (e.g., returned from the boundarymarkers 200).

Detectors 193, 197 can be specifically tuned to detect boundary markers200 and thus dedicated to determining robot positioning within theenvironment, while detectors 190, 194 can be tuned to detect nearbyobstacles within the environment. The front detectors 193 and 190 couldbe stacked on top each other, as can the rear detectors 196, 197.

In further implementations, the front emitter 190 can actually beconfigured as two emitters 190, 191. Each emitter can be specially tunedto emit a high or lower power level, rather than modifying a singleemitter to change its power. Similarly, the rear emitter 194 canactually be configured as two emitters 194, 195.

In other implementations, a single detector on the front 190 and back196 can be used. The controller 150 can adjust the gain up and down incoordination with the expected strength of the detected signals.

One variation which can be used with embodiments including laserradiation accounts for terrain variations that can cause robot lawnmower10 to change its pitch, i.e., tilt the robot body 100 up and down, asthe robot lawnmower 10 traverses the lawn 20. These variations can makethe laser miss the boundary markers by looking too high or too low.Additionally, laser signals are typically emitted as discrete signals,which might miss a boundary marker if the laser has positionally scannedby the boundary marker between successive laser pulses. To increase thelikelihood of the emitted laser beam encountering a boundary marker, thelaser signal can be fanned out into a plane.

Referring to FIGS. 8A-8B, the emitters 190, 194 can be configured to fanthe emitted laser signal 182 horizontally, producing a planar lasersignal that extends out left and right relative to the robot body 100.As the signal 182 sweeps out over a 2D plane, discrete pulses of theplanar signal are much more likely capture a boundary marker 200. In oneexample, a passive optical component can be placed in front of the laserbeam and provide beam shaping. For example, a cylindrical lens or arrayof lenses can be used to generate a fanned beam from the laser. In someexamples, the optical component can generate a fanned beam having anangular width that is between 5 degrees and 10 degrees.

In an alternate embodiment, referring to FIGS. 9A-9B, the emitters 190,194 can be configured to fan the emitted laser signal 182 vertically,producing a planar signal that extends up and down. A vertically fannedsignal is advantageously more likely to hit a boundary marker 200 sincethe up and down signal will encounter the boundary marker 200 regardlessof the up and down and pitch of robot body 100. In one example, apassive optical component can be placed in front of the laser beam andprovide beam shaping. For example, a cylindrical lens or array of lensescan be used to generate a fanned beam from the laser. In some examples,the optical component can generate a fanned beam having an angular widththat is between 5 degrees and 10 degrees.

Referring to FIGS. 10A-10B, the emitters 190, 194 can be configured tofan the emitted laser at an angle 45° relative to both the horizontaland vertical. The resulting diagonal laser planar signal 182 includesthe benefits of both horizontal and vertical laser sheets, by increasingthe likelihood of discrete pulses of the laser hitting the boundarymarker 200 and the pitch of the robot body 100 not impacting the abilityof the laser signal 182 to hit the boundary marker 200. In one example,a passive optical component can be placed in front of the laser beam andprovide beam shaping. For example, a cylindrical lens or array of lensescan be used to generate a fanned beam from the laser. In some examples,the optical component can generate a fanned beam having an angular widththat is between 5 degrees and 10 degrees.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of the disclosure or of what maybe claimed, but rather as descriptions of features specific toparticular implementations of the disclosure. Certain features that aredescribed in this specification in the context of separateimplementations can also be implemented in combination in a singleimplementation. Conversely, various features that are described in thecontext of a single implementation can also be implemented in multipleimplementations separately or in any suitable sub-combination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multi-tasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the embodiments described above should not be understoodas requiring such separation in all embodiments, and it should beunderstood that the described program components and systems cangenerally be integrated together in a single software product orpackaged into multiple software products.

Accordingly, other embodiments are within the scope of the followingclaims.

1-16. (canceled)
 17. A method of estimating a location of a lawn mowingrobot in an environment, the method comprising: positioning a pluralityof synthetic surfaces at known locations with respect to a mowable spacein the environment; and placing a lawn mowing robot in the environment,the lawn mowing robot comprising: a radiation source coupled to the lawnmowing robot; a detector coupled to the lawn mowing robot and configuredto detect radiation reflected by objects in the environment; and acontroller configured to controllably direct radiation from theradiation source to scan the environment, and to vary at least one of anoutput power of the directed radiation and a scan rate of the directedradiation as a function of detected radiation reflected from one or moreof the synthetic surfaces.
 18. The method of claim 17, wherein thecontroller is configured to vary the scan rate of the radiation source.19. The method of claim 17, further comprising a modulator coupled tothe radiation source and configured to modulate radiation emitted fromthe radiation source.
 20. The method of claim 19, wherein the controlleris configured to direct the modulator to vary the output power of theradiation source in response to detection of reflected radiation. 21.The method of claim 20, wherein the modulator scans a portion of asecond scan at a scan speed different from at least a portion of thescan speed of a first scan.
 22. The method of claim 19, wherein thecontroller scans the environment during a motion of the lawn mowingrobot. 23-29. (canceled)
 30. The method of claim 21, wherein the scanspeed of the second scan is slower than the scan speed of the firstscan.
 31. The method of claim 20, wherein the controller is configuredto direct the modulator to vary a radiation beam focus in response todetection of reflected radiation.
 32. The method of claim 17, furthercomprising scanning the environment by rotating a portion of theradiation source.
 33. The method of claim 17, further comprising:comparing, by the controller, data indicative of detected reflectedradiation to stored data; and identifying a particular object asreflecting radiation from the comparison.
 34. The method of claim 17,further comprising modulating the output power of the radiation source.35. A method of estimating a location of a lawn mowing robot in anenvironment, the method comprising: positioning a plurality of syntheticsurfaces at known locations with respect to a mowable space in theenvironment; scanning a radiation source coupled to a lawn mowing robotpresent in the environment; receiving radiation, by one or moredetectors of the lawn mowing robot, reflected by objects in theenvironment; and varying an output power of the directed radiation as afunction of the radiation reflected from one or more of the syntheticsurfaces; varying a scan rate of the directed radiation, as a functionof detected radiation reflected from one or more of the syntheticsurfaces; and estimating a location of the lawn mowing robot.
 36. Themethod of claim 35, wherein the radiation source is a laser.
 37. Themethod of claim 35, further comprising varying a beam focus of theradiation source as a function of detected radiation reflected from oneor more of the synthetic surfaces.
 38. The method of claim 35, whereintwo or more detectors responsive to different wavelengths are employedto detect radiation.
 39. The method of claim 35, wherein scanningcomprises rotating a portion of the radiation source.